As computers grow in speed and shrink in size, power consumed within the computer per unit volume (power density) increases dramatically. Thus, it becomes essential to dissipate the heat generated by components within the computer during operation to ensure that the components remain within their normal operating temperature ranges, since otherwise the components will fail immediately or will have too short a lifetime.
One of the most effective techniques of dissipating heat from a component of a computer is to directly apply a relatively high velocity air flow across the surface of the component to force cool the component. This raises the convective heat transfer coefficient for the surface of that component, thereby increasing the convection cooling. Most computers are provided with fans to promote force cooling, thus increasing the temperature differential between the surface of the component and the surrounding air to increase the efficiency of the heat transfer.
Of all components in a computer, the microprocessor central processing unit ("CPU") liberates the most heat during operation of the computer. It has therefore become common practice to provide a heat sink for the CPU to increase the heat-dissipating surface area for more effective cooling. In addition to the heat sink associated with the CPU, a dedicated CPU cooling fan is often used to provide force cooling and air exchange to dissipate the heat generated by the CPU. Typically, such a fan-based system incorporates a small, axial, box fan driven by a motor.
Although a fan-based system provides effective component cooling, it has draw-backs. For example, if the fan fails or locks up, there is no way to cool the CPU of the computer because there is no back-up capability. Thus the CPU may overheat causing destruction of the CPU and computer failure. A viable solution in this regard is to incorporate a secondary, redundant fan to protect the components of the computer from overheating should the primary fan fail. The redundant fan is usually designed to run continuously with the primary fan while the computer is in standard operation since it has the advantage of offering additional cooling while simultaneously fulfilling the ultimate objective for implementing the other fan.
In these arrangements, each fan moves a portion of the air being used for cooling, and the design is usually such that the total cooling capacity of the fans is greater than minimally necessary to cool the computer. Thus if a single fan fails, the airflow created by the remaining functioning fan or fans is intended to be sufficient to cool the system. However, according to these designs, if one fan fails the airflow pattern is changed since air will continue to move past the heat generating components near the fans still operating. However, the airflow past the components closest to the failing fan may be considerably reduced, or may even be reversed due to back pressures, thus creating hot spots and interfering with the air flow through the operating fans.
Accordingly, what is needed is a computer having an internal fan-based cooling system in which a single fan failure does not unduly compromise air exchange or directionality of air flow, thereby maintaining effective force-cooling of specified components.